The invention relates to an arrangement for the regulation of the charging pressure of an exhaust gas turbocharger consisting of a turbine and compressor of an internal combustion engine in which the exhaust gas stream coming from the internal combustion engine is adapted to be selectively conducted to the turbine or by way of a by-pass line having a by-pass valve around the turbine to the exhaust gas system, and in which the by-pass valve is adapted to be acted upon with control pressure by an electromagnetic timing valve which is connected both to the pressure side and also to the suction side of the compressor and whose timed cycle duration is variable by a control apparatus in dependence on the deviation of the measured charging pressure from the desired charging pressure stored in the control apparatus.
Such an arrangement is disclosed in the DE-OS No. 32 05 009. The turbine of an exhaust gas turbocharger is acted upon with the exhaust gas stream coming from the internal combustion engine; the turbine, in its turn, drives a compressor for supplying charging air for the cylinders. A by-pass valve is inserted into an exhaust gas by-pass line whereby the exhaust gas flow is adapted to be conducted entirely or partly around the turbine directly into the exhaust gas system by opening the by-pass valve. The passage opening of the by-pass valve is controllable by a valve body secured at a diaphragm. The diaphragm is spring-loaded on one side by a spring and is acted upon on the other side with the control pressure which is supplied by an electro-magnetic timing valve. Charging pressure of the charging air supplied by the compressor is present on the one side of the timing valve and the atmospheric pressure of the air entering the compressor is present on the other side thereof.
The control pressure results from mixing charging pressure and atmospheric pressure. With zero opening of the timing valve, the control pressure is equal to the charging pressure whereas with full opening, the control pressure is equal to the atmospheric pressure. The opening and closing time ratio of the timing valve operating, for example, at 15 Hz between the open and closed condition is varied by an electronic control apparatus, by means of which the cyclic opening and closing time of the timing valve is varied in dependence on the signals for the charging pressure, for the rotational speed and for the throttle valve position of the internal combustion engine at the input of the control apparatus.
It is the object of the present invention to so further develop a control arrangement of this type that its operating reliability is increased.
The underlying problems are solved according to the present invention in that two control lines are provided each consisting of a timing valve, of a control apparatus and of a control pressure line which are adapted to be activated for controlling the by-pass valve. If two control lines each consisting of a timing valve and of a control apparatus are provided which are both connected to the by-pass valve, a redundant control system is created which increases the operating reliability. In case of failure of the one control line which is just in operation, the other can take over its function. In order to avoid that both control lines operate in common, as a result of which undesired overlap effects or control oscillations could occur, the pressure level at which the two control lines respond, are slightly different. During normal operation, only the one control line operates which is designed for the higher control pressure level. This is achieved in an advantageous construction according to the present invention in that both timing valves are connected by way of separate pneumatic control pressure lines with a switching valve, from which a common control pressure line leads to the by-pass valve. The valve body of the switching valve is so displaced by the higher pressure in the control pressure line of the control system, in which the desired charging pressure is reached, that it closes the other control pressure line, as a result of which the control line coordinated thereto becomes ineffective.
A differing control pressure level can be achieved in that either the desired charging pressure stored in the control apparatus or the actual charging pressure fed to the control apparatus by pressure sensors is different.